The invention relates to a method for suppressing an echo signal in a range finder device, which has at least one light-sensitive receiver and at least one laser light source as a transmitter, with the echo signal to be suppressed being a result of diffuse reflectances of the light emitted by the transmitter at surfaces before the actual target—for example at components of the optical signal path.
Furthermore, the invention relates to a range finder device having at least one light-sensitive receiver and at least one laser light source as transmitter.
In addition, the invention relates to a far-optical device, in particular a telescope or a telescopic sight.
Range finder devices of the generic kind, also referred to as laser range finder, perform a range finding by a laser pulse or pulse trains being emitted by a transmitter, being reflected by the target object, being detected by a receiver and the period of time and thus the covered distance is determined by means of the delay between the transmission pulses and the receiving pulses.
Transmitter and receiver of a range finder device of the generic kind can be arranged at least partially in one optical path. If transmitter and receiver are arranged within one and probably even attached to one and the same (prism) optics, as for example known from document WO 2009094687 A2, it can occur that a small portion of the laser pulses emitted by the transmitter reach the sensitive receiver directly due to internal scattering, reflection etc. thus generating a test signal. This incorrect test signal is usually larger than the signals from a target object further away and therefore interfere with/manipulate the measurement. Since said flare is almost always present at first, only measurements within the close range (up to some 100 m) are affected. The term interfering echo signal in this document refers to all portions of the light emitted by the transmitter, which portions have arrived at the receiver due to internal reflections, scatterings or other parasitic errors.
The optical cross talk can be influenced by constructional measures (e.g. diaphragms, geometry). In terms of electronics this can be defined by e.g. a first time window, when e.g. the receiver and the amplifier are not active, since the cross talker is present here. Only after this window has expired, a range finding is carried out. The disadvantage is here that within this window, no measurement can be carried out at all. In the document U.S. Pat. No. 7,599,045 B2, this ‘blind’ window is realized by the detecting signal inverting the portion branched off and lying within said window and adding it to the test signal again, with the result that the sum signal is zero again. The disadvantage of the known embodiment is that due to the ‘blind’ window only ranges of considerably more than 100 m can be measured.